As it is widely known, it is common practice to use, for such an engine type, an intake air that is compressed, generally referred to as supercharging air, for feeding its cylinders. This allows to increase the power of this engine that is intrinsically dependent on the amount of air allowed into the combustion chamber of these cylinders.
It is also known to increase even further the power of this type of engine by carrying out an operation referred to as burnt gas scavenging. It consists in discharging, at the start of the intake phase of this engine, the residual exhaust gases contained in the combustion chamber at the end of the exhaust phase in order to replace them by supercharged air. This operation is generally carried out by overlap of the exhaust and intake valves.
The problem of transfer of the carbureted supercharged air directly to the exhaust upon valve overlap arises during this scavenging operation. In fact, during this transfer, part of the carbureted supercharged air is discharged through the engine exhaust and sent to the atmosphere. This discharge sends unburnt hydrocarbons, which are pollutants harmful to the environment and to mankind, in the ambient air.
In order to prevent such a problem, in French patent application No. 2,841,294 filed by the applicant, the burnt gas scavenging operation is carried out by adding and using an additional intake pipe with its valve, specifically to introduce non-carbureted supercharged air.
This type of device thus consists of a specific intake pipe (with its valve) for introduction of the non-carbureted supercharged air used during the scavenging operation in the combustion chamber and of another intake pipe, also with its valve, for allowing carbureted supercharged air upon closure of the specific intake pipe.
Thus, the burnt gas scavenging operation is carried out by overlap of the exhaust valve and of the non-carbureted supercharged air intake valve of the cylinder considered. During this overlap, the non-carbureted supercharged air allowed into the combustion chamber replaces the residual burnt gases that are discharged through the exhaust valve to the exhaust manifold, then the exhaust line.
Once this scavenging operation complete, the other intake pipe is used to prepare a fuel mixture in the combustion chamber.
This also poses a not insignificant problem because the inlets of the carbureted supercharged air and non-carbureted supercharged air intake pipes are generally connected to a single intake distributor.
Mixing between the carbureted supercharged air from the carbureted supercharged air pipes and the non-carbureted air from the non-carbureted supercharged air intake pipes therefore occurs within this distributor. Consequently, during the burnt gas scavenging operation, partly carbureted supercharged air is fed into the combustion chamber prior to being discharged through the exhaust valve with the burnt gases.
This also leads to an unburnt hydrocarbon discharge to the exhaust and to fuel overconsumption.
Furthermore, it may be desired to modify the engine efficiency, notably by changing the compression ratio. One of the two intake valves is therefore kept in open position, generally the carbureted air valve, at the start of the engine compression phase and for some crank angle degrees.
The fuel mixture present in the combustion chamber is therefore not compressed at the start of the engine compression phase and the compression ratio can be modified depending on the closing time of this intake valve. However, carbureted air is fed into the intake pipe and the aforementioned problem remains, with the possibility of mixing with the non-carbureted air used for scavenging.
The present invention thus aims to overcome the aforementioned problems by means of a method of controlling the intake of a supercharged internal-combustion engine that allows to carry out the burnt gas scavenging operation under conditions minimizing the discharge of unburnt hydrocarbons, for a direct-injection as well as an indirect-injection engine, while keeping the engine performances.